When golfers swing a golf club, a behavior of the golf club is varied in accordance with force applied from the golfers to the golf club. Although golfers have different conditions for an ideal golf club, one condition of particular importance may be a high head speed of the golf club when the golfers swing the golf club. The reason is that the high head speed makes it possible to easily achieve a long flying distance.
Conventionally, as a method for selecting, for each golfer, a golf club that would increase the head speed, it has been proposed to calculate a deformed shape of a shaft included in a golf club during a swing of the golfer and grasp a feature of the swing of the golfer, and to subsequently select an optimal shaft for the golfer. (For example, refer to Patent Literature 1.) In the selection method described in Patent Literature 1, a bending moment generated in the shaft during a swing of a golfer is calculated based on a bending amount measured by a strain gauge attached to the golf club, and with use of EI (bending rigidity) distribution of the shaft of the golf club calculated in advance and various other parameters of the golf club shaft, a deformation behavior of the shaft during the swing is analyzed. Furthermore, in the selection method described in Patent Literature 1, the deformation behavior obtained by the analysis is classified into a predetermined pattern, and a golf club shaft having EI distribution suitable for the golfer may be selected.